The National Library of Medicine's Unified Medical Language System Project (UMLS) is a ongoing project to overcome the lack of links between the different classification and representation schemes used in biomedical information sources including those for biomedical literature, for patient records, for biomedical databanks, and for medical knowledge bases. Major information sources are available in a wide variety of automated systems, but health care professionals and biomedical researchers have no means to access and integrate the information they need for patient care and for research. The UMLS project is building links to allow interactive or automated searches across the wide variety of presently available biomedical information sources. The UMLS Metathesaurus is the central vocabulary component of the Project. It contains, links, and categorizes terms from biomedical vocabularies and classifications used for biomedical literature, for patient records, and for health care procedures. The first version of the Metathesaurus, named Meta-1, will be issued to developers and biomedical information professionals within a few weeks. Project Objectives for this contract are for the identification of useful and feasible enhancements to the Metathesaurus. These enhancements will be targeted in tasks for including additional terms and concepts from vocabularies already represented in Meta-1, to improve the breadth and depth of subject linkage; for incorporating additional vocabularies in whole or in part, to eliminate gaps in subject coverage; for adding additional types of information for terms already a part of Meta-1, to improve searching utility; and for the modification of the structure of Metathesaurus records, to enhance their utility for searchers or to improve the ongoing maintenance, updating, and expansion of the Metathesaurus.